CN1176563C - Dynamic channel allocating method - Google Patents

Abstract

The invention discloses a dynamic channel allocation (DCA) method of a TDD-CDMA mobile communication system, which is to classify the mobile station MS according to the distance from the base station BS of the cell, and in the same code channel group (carrier frequency + time slot) The code channel is assigned to the mobile station MS with a similar distance; at the same time, MSs with different distances have different requirements for transmission power and interference to adjacent cells. The system determines whether the MS can use the cross slot according to the transmission power requirements of the MS. The code channel group and the code channel group of which multiplexing factor is used. By adopting the method of the invention, the interference can be effectively avoided, the capacity can be increased, and the networking of the TDD-CDMA system can be easily realized.

Description

Dynamic Channel Allocation Method

technical field

The invention relates to the technical field of code division multiple access (CDMA) mobile communication, in particular to a dynamic channel allocation method in a time division duplex-code division multiple access (TDD-CDMA) system.

Background technique

In time division multiple access (TDMA) and frequency division multiple access (FDMA) communication systems, the channels themselves are orthogonal, and there is no need to consider the interference between channels. The dynamic channel allocation (DCA) of TDMA and FDMA communication systems is relatively simple, and only need to consider the most compact channel multiplexing method in terms of distance while satisfying co-channel interference. And in the process of considering this problem, the worst case is always assumed, that is, the implicit assumption is that the distance between the mobile station and the base station is the radius of the cell, which will inevitably lead to a reduction in spectral efficiency. In the frequency division duplex-code division multiple access (FDD-CDMA) system, since the uplink and downlink use two carrier frequencies, there is no mobile station-mobile station (MS-MS) and base station-base station (BS-BS) interference, the DCA scheme it adopts is also relatively simple.

The uplink (UL) and downlink (DL) of the TDD-CDMA system use the same carrier frequency, which can meet the needs of asymmetric services. The possible inconsistency of the service types of each cell leads to the generation of cross time slots. A cross-slot refers to a time slot in which a cell is in the uplink and/or downlink, while its adjacent cells are in the downlink and/or uplink. In the TDD-CDMA system, there are four kinds of inter-cell interference: BS-to-MS interference and MS-to-BS interference in non-crossed time slots, MS-to-MS interference and BS-to-BS interference in crossed time slots. Especially the interference in the cross-slot, because the BS transmit power and receive gain are relatively high, and two MSs may be very close, so the interference is very serious, which will bring difficulties to the system networking.

Contents of the invention

In view of the fact that the above-mentioned TDD-CDMA system can realize asymmetric services, but may cause serious inter-cell interference at the same time, the purpose of the present invention is to provide a dynamic channel allocation (DCA) method of a TDD-CDMA system, which can reduce interference, increase Capacity, convenient system networking.

A dynamic channel allocation method of a TDD-CDMA mobile communication system of the present invention is that the mobile stations are classified according to the distance from the base station of the cell, and the code channels in the same code channel group are assigned to the mobile stations with similar distances; Track groups allow different multiplexing factors.

According to the above-mentioned technical solution of the present invention, the code channel group is divided into three groups according to the distance between the mobile station and the base station from the farthest to the farthest, which are the cross-slot code channel group, the low-power code channel group and the high-power code channel group. group; and a multiplexing factor of 1 is used for the low-power code channel group, and a multiplexing factor of less than 1 is used for the high-power code channel group.

According to the distance between the mobile station and the base station of the cell, it is determined whether the code channel of the cross-slot code channel group can be allocated to the mobile station or the code channel of the code channel group of which reuse factor can be allocated to the mobile station. Specifically, the following steps may be included:

(a) The base station first determines two distances α·r and β·r according to the system requirements, where r is the radius of the cell, and α<β<1;

(b) After the base station receives the channel request from the mobile station, judge the distance d between the mobile station and the base station;

(c) If d<α·r, then search for idle code channels in the cross-slot code channel group, low-power code channel group and high-power code channel group in order to allocate;

(d) If α r<d<β r, then search for idle code channels in the low-power code channel group and the high-power code channel group in order to allocate;

(e) If d>β·r, search for idle code channels in the high-power code channel group for allocation.

In the above-mentioned method of the present invention, it is 1 to be assigned to the code channel group of the mobile station of the distance d＜β r assigned to the base station; Channel groups and handover reserved channels use a multiplexing factor less than 1.

The one code channel group refers to the code channels in one carrier frequency plus time slot combination.

The DCA method of the TDD-CDMA system of the present invention classifies according to the distance between the mobile station and the base station, and distributes the code channels in one code channel group to the mobile stations with similar distances; at the same time, according to the interference of different code channel groups to adjacent cells Different levels of multiplexing use different multiplexing factors, which can effectively avoid interference, increase capacity, and make the networking of TDD-CDMA systems easy to implement.

Description of drawings

FIG. 1 is a schematic diagram of a frame structure of an embodiment of the present invention.

FIG. 2 is a schematic diagram of cell distribution in an embodiment of the present invention.

FIG. 3 is a schematic flow chart of an embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the TDD-CDMA system, the operator may have multiple carrier frequencies, and each carrier frequency has multiple time slots in one frame, and each time slot is divided into several code channels by spreading codes. Here, a combination of a carrier frequency and a time slot is defined as a code channel group. Due to the guard bands between carrier frequencies and the guard time between time slots, the interference between code channel groups can be ignored.

During the propagation of electromagnetic waves in space, their power attenuates with the increase of distance. Therefore, the MS that is far away from the BS needs a larger transmit power, both uplink and downlink. At the same time, the distance between the MS and a neighboring cell must be relatively short, and the interference to it must be relatively large. On the contrary, the MS that is closer to the BS requires less transmit power and is farther away from adjacent cells, so the interference caused is also smaller. The TDD-CDMA system dynamic channel allocation method proposed by the present invention classifies users according to the distance between MS and BS, and arranges users with close distances in the same code channel group. In this way, firstly, the interference between cells is reduced: for code channel groups arranged with close-distance users, if the distance between adjacent cells satisfies the minimum reuse distance of the channel, then the interference between adjacent cells can be ignored; secondly, it reduces Multiple access interference in the cell: If there are short-distance users and long-distance users in a code channel group, in the downlink phase, the long-distance users will cause strong multiple-access interference to short-distance users; due to the result of power control, the This leads to an increase in the transmit power of close-distance users, which in turn leads to the enhancement of interference to adjacent cells.

Assuming that the radius of the cell is r, two distances can be determined according to system requirements during specific implementation: αr and β·r, where α<β<1.

First of all, due to the interference between BS-BS and MS-MS that is unique to TDD in the cross-slot, the cross-slot is arranged for short-distance users. On the one hand, the transmission power of the transmitter is small, and on the other hand, The situation that two MSs are very close is avoided, which can effectively avoid interference. That is, the code channel group in the cross-slot is only assigned to the users whose distance from the base station is <α·r.

Secondly, different reuse factors are used according to the degree of interference of different code channel groups to adjacent cells:

A reuse factor of 1 is used for the code channel group allocated to users whose distance from the base station is <βr, because the interference of the transmission power required by users whose distance from the base station is <βr to adjacent cells can meet the system requirements, and all cells can Use the same channel group;

For a certain number of code channel groups, the reuse factor is less than 1, which is used for users whose distance from the base station is greater than βr and to switch reserved channels. This is because the MS that is far away from the BS requires relatively large transmission power, which will inevitably cause damage to adjacent cells. Interference can be avoided by adopting a reuse factor of less than 1 for the code channel group arranged for long-distance users. The cell in the interference area does not use the code channel group, and the code channel group can be reused outside the interference area.

An example of dynamic channel allocation in a specific TD-SCDMA system is given below.

An operator has 3 carrier frequencies, marked as C1, C2, and C3 respectively. The subframe structure of the system is shown in Figure 1. A subframe has 7 standard time slots, which are marked as Ts0~Ts6 respectively, where Ts0 must be the downlink time slot, Ts1 must be the uplink time slot, and there is a time slot between Ts2~Ts5. The position of the conversion point from uplink to downlink can be set according to business needs. A channel group is marked with C#Ts#. Consider three cells in the communication system, as shown in Figure 2. Assume that according to service requirements, see Table 1 for the division of the uplink and downlink time slots of the three cells on each carrier frequency.

Table 1 Carrier frequency 1 carrier frequency 2 Carrier frequency 3 Uplink downlink Uplink downlink Uplink downlink Cell 1 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Cell 2 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Cell 3 Ts1 Ts2Ts3 Ts4 Ts5Ts6 Ts0 Ts1 Ts2 Ts3 Ts4Ts5 Ts6Ts0 Ts1 Ts2 Ts3 Ts4Ts5 Ts6Ts0

The setting of each cell on carrier frequency 1 is the same, there is no cross time slot, and Ts3 of carrier frequency 2 and carrier frequency 3 is a cross time slot. The high-power code channel group, cross-slot code channel group and low-power code channel group used by each cell are shown in Table 2, Table 3 and Table 4 respectively. Among them, the multiplexing factor used by the high-power code channel group is 1/3, the multiplexing factor used by the low-power code channel group is 1, and the cross-slot code channel group can only be used by mobile stations that meet the cross-slot interference requirements of adjacent cells. use.

Table 2 High-power code channel groups of each cell Uplink downlink Cell 1 C1Ts1, C1Ts0 Cell 2 C2Ts1 C2Ts0 Cell 3 C3Ts1 C3Ts0, C3Ts6

Table 3 Cross-slot code channel groups of each cell Uplink downlink Cell 1 C2Ts3, C3Ts3 Cell 2 C2Ts3, C3Ts3 Cell 3 C2Ts3, C3Ts3

Table 4 Low-power code channel groups of each cell Uplink downlink C1Ts2, C1Ts3, C2Ts2, C3Ts2 C1Ts4, C1Ts5, C1Ts6, C2Ts4, C2Ts5, C2Ts6, C3Ts4, C3Ts5

The process of dynamic channel allocation to channel request response is shown in Figure 3:

(a) The mobile station initiates a channel request;

(b) The base station receives the channel request from the mobile station and determines the distance d between the mobile station and the base station;

(c) Judging that d<α·r? If so, search for idle code channels in the cross-slot code channel group, low-power code channel group and high-power code channel group for allocation; otherwise

(d) Judging that α·r<d<β·r? If so, search for idle code channel allocation in the low-power code channel group and high-power code channel group in turn; otherwise

(e) Search for idle code channel allocation in the high-power code channel group for allocation.

One of the advantages of the TDD-CDMA system is that it adopts the TDD mode of time division duplexing, which can meet the needs of asymmetric services, but the interference of MS-MS and BS-BS between adjacent cells caused by this has a negative effect on the network. The DCA method provided by the present invention is one of the key technologies to solve this difficulty. In TDMA and FDMA communication systems, the channels themselves are orthogonal, so there is no need to consider the interference between channels. The DCA of TDMA and FDMA communication systems is relatively simple, and only needs to consider the channel to obtain the most compact reuse method in terms of distance. In FDD-CDMA, since the uplink and downlink use two carrier frequencies, there is no MS-MS and BS-BS interference, and the DCA scheme adopted is relatively simple. However, the uplink and downlink of TDD-CDMA use one carrier frequency, which brings additional interference and requires a more complex DCA scheme. In the DCA method of the present invention, MSs are classified according to the distance from the base station, and the code channels in one code channel group are allocated to MSs with similar distances. At the same time, different reuse factors are adopted according to the degree of interference of different code channel groups to adjacent cells, which is different from the previous use of the same reuse factor for all channels in a cell. By adopting the DCA method of the invention, interference can be effectively avoided, capacity can be increased, and the networking of the TDD-CDMA system can be realized more easily.

The present invention classifies the mobile station MS according to the distance from the base station BS of the cell, and assigns the code channels in the same code channel group (carrier frequency+time slot) to the mobile station MS with similar distances; The power requirements are different, and the interference to adjacent cells is also different. The system determines whether the MS can use the cross-slot code channel group and which code channel group uses the multiplexing factor according to the MS's requirements for transmit power. Any modifications, equivalent replacements, improvements, etc. made within the above spirit and principles of the present invention shall be included within the scope of the claims of the present invention.

Claims (5)

1, a kind of dynamic channel assignment method of TDD-CDMA mobile communication system is characterized in that this method comprises:

According to classifying, and distribute the code channel in the same code channel group to give distance close travelling carriage travelling carriage with the distance of this cell base station; Simultaneously different code channel groups allows to adopt the different multiplexing factors;

Wherein, a described code channel group is that a carrier frequency adds the code channel in the time slot combination.

2, dynamic channel assignment method according to claim 1 is characterized in that: described code channel group is divided into three groups from the near to the remote according to the distance of travelling carriage and base station, is respectively cross time-slot code channel group, low-power code channel group and high power code channel group; And low-power code channel group is adopted the multiplexing factor is 1, adopts the multiplexing factor less than 1 to high power code channel group.

3, dynamic channel assignment method according to claim 2 is characterized in that this method further comprises: the distance according to travelling carriage and this cell base station determines whether to distribute the code channel of cross time-slot code channel group to give this travelling carriage for the code channel of the code channel group of this travelling carriage or which kind of multiplexing factor.

4, dynamic channel assignment method according to claim 3 is characterized in that this method specifically comprises:

(a) determine two distance alpha r and β r according to system requirements, wherein r is a radius of society, α＜β＜1;

(b) after the channel request of travelling carriage is received in the base station, judge travelling carriage and base station apart from d;

(c) if d＜α r, then preface is sought idle code channel respectively and is distributed in cross time-slot code channel group, low-power code channel group and high power code channel group successively;

(d) if α r＜d＜β r, then preface is sought idle code channel respectively and is distributed in low-power code channel group and high power code channel group successively;

(e) if d＞β r then seeks idle code channel and distributes in high power code channel group.

5, dynamic channel assignment method according to claim 4 is characterized in that this method further comprises: to adopt the multiplexing factor be 1 to distributing to the code channel group apart from the travelling carriage of d＜β r with the base station; To distribute to the base station apart from the code channel group of the travelling carriage of d＞β r and switch and keep channel and adopt the multiplexing factor less than 1.